Physical and Technical Institute

In this review we discuss considerations regarding the common techniques used for measuring thermoelectric transport properties necessary for calculating the thermoelectric figure of merit, <italic>zT</italic>.

Abstract The basic properties of electric polarization response in crystalline dielectrics are theoretically analysed. Spontaneous polarization, pyroelectricity, piezoelectricity, flexoelectricity (polarization response to strain gradient) and thermopolarization effect (polarization response to temperature gradient) are discussed on the basis of a unified approach. Special attention is paid to the problem of the adequate theoretical definition of these phenomena. The effect of the sample termination on the polarization response is considered in detail. Key Words: Electric polarizationthermal perturbationselastic perturbationsdielectrics

Synopsis This paper is a sequel to [1-4]. We consider the problem of G-closure, i.e. the description of the set GU of effective tensors of conductivity for all possible mixtures assembled from a number of initially given components belonging to some fixed set U . Effective tensors are determined here in a sense of G-convergence relative to the operator ∇· D · ∇, of the elements DeU ∈ [5, 6]. The G-closure problem for an arbitrary initial set U in the two-dimensional case has already been solved [3, 4]. It remained, however, unclear how to construct, in the most economic way, a composite with some prescribed effective conductivity, or, equivalently, how to describe the set G m U of composites which may be assembled from given components taken in some prescribed proportion. This problem is solved in what follows for a set U consisting of two isotropic materials possessing conductivities D + = u + E and D − = u − E where 0&lt;u − &lt;u + &lt;∞ and E ( = ii+jj) is a unit tensor.

Properties of the perovskite ferroelectrics Na0.5Bi0.5TiO3 (NBT), K0.5Bi0.5TiO3 (KBT) and their solid solutions are reviewed. Consideration of the NBT behavior draws attention to phenomena of the ion ordering, coexistence of several phase regions within a crystal lattice, phase transition diffusion and to a quite new phenomenon: existence of the isotropization points (temperatures) in the AFE-phase-temperature interval. In the KBT the isotropic points are absent. NBT, KBT, and their solid solutions are considered as possible useful materials for technical (in particular, for piezoelectric) applications. There are also some other A0.5 +Bi0.5B4+O3 perovskites which are interesting for future research. Keywords: Ferroelectricsperovskites A0.5 +Bi0.5TiO3

The variation in the expression patterns of the gap genes in the blastoderm of the fruit fly Drosophila melanogaster reduces over time as a result of cross regulation between these genes, a fact that we have demonstrated in an accompanying article in PLoS Biology (see Manu et al., doi:10.1371/journal.pbio.1000049). This biologically essential process is an example of the phenomenon known as canalization. It has been suggested that the developmental trajectory of a wild-type organism is inherently stable, and that canalization is a manifestation of this property. Although the role of gap genes in the canalization process was established by correctly predicting the response of the system to particular perturbations, the stability of the developmental trajectory remains to be investigated. For many years, it has been speculated that stability against perturbations during development can be described by dynamical systems having attracting sets that drive reductions of volume in phase space. In this paper, we show that both the reduction in variability of gap gene expression as well as shifts in the position of posterior gap gene domains are the result of the actions of attractors in the gap gene dynamical system. Two biologically distinct dynamical regions exist in the early embryo, separated by a bifurcation at 53% egg length. In the anterior region, reduction in variation occurs because of stability induced by point attractors, while in the posterior, the stability of the developmental trajectory arises from a one-dimensional attracting manifold. This manifold also controls a previously characterized anterior shift of posterior region gap domains. Our analysis shows that the complex phenomena of canalization and pattern formation in the Drosophila blastoderm can be understood in terms of the qualitative features of the dynamical system. The result confirms the idea that attractors are important for developmental stability and shows a richer variety of dynamical attractors in developmental systems than has been previously recognized.

Abstract The most serious defect of the modern theory of metals is the very unsatisfactory manner in which it takes account of the forces of interaction between the valency electrons of the metal. This is well shown in the anomalies characteristic of the electrical properties of the ferromagnetics; from the standpoint of Bloch’s theory they are quite inexplicable, as the criterion of ferromagnetism itself can be formulated only in the language of a more accurate theory which takes account of the exchange effects. The problem of construction such a systematic theory of metals, which could enable us to treat their electric and magnetic properties simultaneously, reduces itself substantially to choosing a suitable approximation scheme. At first sight it would seem most natural to us the scheme applied so successfully by Heisenberg in explaining the phenomena of ferromagnetism. Here the metal is considered, in the zero approximation, as an assembly of isolated electrically neutral atoms; in the following approximations, account is taken of the interaction of the valency electrons not only with the ions of the metal but also with each other. In his Leipzig Report, Bloch asserts that such a scheme affords an adequate tool for dealing with all the characteristic properties of metals, in particular with the electrical conduction. We are, however, of the opinion that this assertion is incorrect, and that, in reality, Heisenberg’s approximation cannot be used in the theory of electrical conduction simply because, in this approximation, the metal is not a conductor. In fact, it can be proved in quite a general manner (for special cases it has already been proved by Slater), that in all the stationary states of Heisenberg’s scheme the total current carried by the valency electrons of the metal is equal to zero; this result does not depend on any one special property of the perturbation equations, but simply follows from the fact that only the non-polar states of the system are chosen as zero approximation, i. e., only those states in which each atom of the metal is electrically neutral. Such a theory considers only those transitions of electrons from one atom to another, in which two electrons simultaneously change places (i. e., only the exchange processes); such transitions cannot of course give rise to an electric current.

Abstract The properties of amorphous materials determined by the presence of localized atomic and electronic states are reviewed. Experimental data on atomic dynamics in glasses are described. The two-level-system (TLS) model is presented, and the limits of its applicability analysed. The concept of soft atomic potentials, allowing generalization of the TLS model to higher energies, is introduced. Atomic dynamics in soft potentials, as well as soft-potential coupling with phonons and thermal expansion of glasses, are described. Localized electronic states in glasses are investigated and different theoretical models of such states in glassy semiconductors are reviewed. The connection between localized electronic states and soft potentials is studied. Particular attention is paid to low-relaxation processes in glasses controlled by two-well soft potentials; specifically, low-frequency noise in disordered conductors is considered. The possibility of investigating the localized states in question with the help of point-contact spectroscopy is discussed.

Abstract The results of an investigation of a large group of diffuse phase transition ferroelectrics distinguished by a number of specific features that make them important for both research and application are reported. A mechanism for diffuse phase transition is proposed. The necessity of a theory for this class of disordered and non-equilibrium systems is pointed out.

Coulomb blockade in a system of two dots connected in series is qualitatively different from that of a single dot. We show that, although the conductance G of a double-dot system reveals oscillations with the gate-induced potential ${\mathit{V}}_{\mathit{g}}$, a typical period of these oscillations changes with the temperature. If the capacitance ratio ${\mathit{C}}_{1}$/${\mathit{C}}_{2}$ for the dots is an irrational number, the system of peaks in G(${\mathit{V}}_{\mathit{g}}$) becomes increasingly sparse as the temperature decreases. Both the peak-to-peak distance and the activation energies of the conductance at the peaks that persist are random. However, the distribution function of activation energies calculated for a large interval of ${\mathit{V}}_{\mathit{g}}$ has a universal shape and may be considered as a characteristic pattern of a double-dot system. If the ratio ${\mathit{C}}_{1}$/${\mathit{C}}_{2}$ is small, there is a substantial range of intermediate temperatures in which the ordinary periodic Coulomb oscillations are restored. Numerical simulations show that for observation of both stochastic and regular Coulomb blockade for the same sample at different temperatures it is enough to have the ratio ${\mathit{C}}_{1}$/${\mathit{C}}_{2}$\ensuremath{\le}0.5. The existence of a small interdot capacitance C\ensuremath{\ll}${\mathit{C}}_{1}$,${\mathit{C}}_{2}$ is shown to cause, at the lowest temperatures, a splitting of the conductance peaks that persist into doublets with a constant spacing ${\mathit{e}}^{2}$C/${\mathit{C}}_{1}$${\mathit{C}}_{2}$.

The dynamic phenomena connected with isolated defects in a lattice and the dynamics of a crystal with various types of defects are examined. Simplified models are used in the interpretation of the results and to assess orders of magnitude of the phenomena.

We present experimental proof that in rotating $^{3}\mathit{B}$ the vortex-core transition temperature ${\mathit{T}}_{\mathit{V}}$ separates axisymmetric vortices above ${\mathit{T}}_{\mathit{V}}$ from vortices with spontaneously broken axial symmetry below ${\mathit{T}}_{\mathit{V}}$. The nonaxisymmetry is observed in the presence of coherent spin precession as a new soft Goldstone mode, manifested as oscillations and spiral twisting of the core anisotropy axis. These are driven by the precessing spin via spin-orbit coupling and lead to magnetic relaxation from viscous losses, which depend on vortex pinning.

Moving branch points in the $j$ plane are investigated on the basis of analysis of multiparticle terms of the unitarity condition in the $t$ channel. A definite assumption about the form of an analytic continuation of these terms into complex $j$ is used. It is shown that in this case in the $j$ plane there arise branch points of the partial amplitude ${f}_{j}(t)$ corresponding to the production thresholds of two or more Regge poles with relative orbital momentum equal to - 1. In the case of two zero-spin particles in the intermediate state, the partial wave has a singularity at negative integral values of the orbital momentum. Azimov has found that such singularities shift to the right if the particles in the intermediate state have nonzero spin. The branch points in the $j$ plane result from the extension of this shift throughout the Regge trajectory. This mechanism of emergence of branch points has been indicated by Mandelstam for the case of Feynman diagrams of a certain class. The presence of these branch points at $j={j}_{n}(t)$ where ${j}_{n}(t)=n\ensuremath{\alpha}(\frac{t}{{n}^{2}})\ensuremath{-}n+1$ changes essentially the analytic properties of ${f}_{j}(t)$ in the $t$ plane, leading to the emergence in the $t$ plane of branch points at $t={t}_{n}(j)$, where ${t}_{n}(j)$ is the solution of the equation $j={j}_{n}(t)$. The discontinuity ${{\ensuremath{\delta}}_{t}}^{(n)}{f}_{j}(t)$ of the amplitude ${f}_{j}(t)$ on the singularity $t={t}_{n}(j)$ corresponding to the $n$-Regge-pole production threshold (Regge-pole unitarity conditions) is calculated. It is shown that this discontinuity has a form similar to the conventional unitarity condition. ${{\ensuremath{\delta}}_{t}}^{(n)}{f}_{j}(t)=(\frac{1}{2i})[{f}_{j}(t+i\ensuremath{\epsilon})\ensuremath{-}{f}_{j}(t\ensuremath{-}i\ensuremath{\epsilon})]$ being given by the product of the amplitudes ${N}_{j,n}$ of production of $n$ Regge poles determined above and under a cut made in the $t$ plane from the point $t={t}_{n}(j)$. The discontinuity ${{\ensuremath{\delta}}_{t}}^{(n)}{f}_{j}(t)$ of the amplitude ${f}_{j}(t)$ across the cut connected with the branch point $t={t}_{n}(j)$ is calculated at $t\ensuremath{\rightarrow}{t}_{n}(j)$. The discontinuity is shown to have the form ${{\ensuremath{\delta}}_{t}}^{(n)}{f}_{j}(t)=\ensuremath{\pi}{B}_{n}{[t\ensuremath{-}{t}_{n}(j)]}^{n\ensuremath{-}2}$. This means that the singularity of ${f}_{j}(t)$ has a logarithmic character, i.e., near it we have ${f}_{j}(t)={A}_{n}+{B}_{n}{[j\ensuremath{-}{j}_{n}(t)]}^{n\ensuremath{-}2}\mathrm{ln}[j\ensuremath{-}{j}_{n}(t)]$, where ${A}_{n}$ and ${B}_{n}$ have no singularities at $j={j}_{n}(t)$. The results obtained will be used elsewhere for analysis of the asymptotic behavior of the diffraction scattering amplitude in the region of not-large values of the momentum transfer.

(1968). Electromagnetic waves in metals in a magnetic field. Advances in Physics: Vol. 17, No. 69, pp. 605-747.

Attention is drawn to a principal difference between the transfer of a horizontal magnetic field by turbulence and by three-dimensional cell convection. If the motion of the conducting medium in the cells is such that the heated material ascends at the centre while descending along the sides of the cells, then the magnetic tubes of force will be carried downwards by peripheral flows. Discrete ascending flows separated from one another by descending material carry only closed magnetic field loops. Such loops do not transfer net magnetic flux. As a result, the magnetic flux becomes blocked at the base of the convective layer.

Infrared reflection measurements of the half-filled two-dimensional organic conductors $\ensuremath{\kappa}\text{\ensuremath{-}}{(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}\mathrm{Cu}[\mathrm{N}{(\mathrm{C}\mathrm{N})}_{2}]{\mathrm{Br}}_{x}{\mathrm{Cl}}_{1\ensuremath{-}x}$ [BEDT-TTF denotes bis-(ethylenedithio)tetrathiafulvalene] were performed as a function of temperature $(5\phantom{\rule{0.3em}{0ex}}\mathrm{K}&lt;T&lt;300\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and Br substitution ($x=0%$, 40%, 73%, 85%, and 90%) in order to study the metal-insulator transition. We can distinguish absorption processes due to itinerant and localized charge carriers. The broad midinfrared absorption has two contributions: transitions between the two Hubbard bands and intradimer excitations from the charges localized on the ${(\mathrm{BEDT}\text{\ensuremath{-}}\mathrm{TTF})}_{2}$ dimer. Since the latter couple to intramolecular vibrations of BEDT-TTF, the analysis of both electronic and vibrational features provides a tool to disentangle these contributions and to follow their temperature and electronic-correlation dependence. Calculations based on the cluster model support our interpretation.

The thermal evolution of young neutron stars (NSs) reflects the neutrino emission properties of their cores. Heinke &amp;amp; Ho (2010) measured a 3.6+/-0.6% decay in the surface temperature of the Cassiopeia A (Cas A) NS between 2000 and 2009, using archival data from the Chandra X-ray Observatory ACIS-S detector in Graded mode. Page et al. (2011) and Shternin et al. (2011) attributed this decay to enhanced neutrino emission from a superfluid neutron transition in the core. Here we test this decline, combining analysis of the Cas A NS using all Chandra X-ray detectors and modes (HRC-S, HRC-I, ACIS-I, ACIS-S in Faint mode, and ACIS-S in Graded mode) and adding a 2012 May ACIS-S Graded mode observation, using the most current calibrations (CALDB 4.5.5.1). We measure the temperature changes from each detector separately and test for systematic effects due to the nearby filaments of the supernova remnant. We find a 0.92%-2.0% decay over 10 years in the effective temperature, inferred from HRC-S data, depending on the choice of source and background extraction regions, with a best-fit decay of 1.0+/-0.7%. In comparison, the ACIS-S Graded data indicate a temperature decay of 3.1%–5.0% over 10 years, with a best-fit decay of 3.5+/-0.4%. Shallower observations using the other detectors yield temperature decays of 2.6+/-1.9% (ACIS-I), 2.1+/-1.0%(HRC-I), and 2.1+/-1.9% (ACIS-S Faint mode) over 10 years. Our best estimate indicates a decline of 2.9+/-0.5stat+/-1.0sys% over 10 years. The complexity of the bright and varying supernova remnant background makes a definitive interpretation of archival Cas A Chandra observations difficult. A temperature decline of 1–3.5% over 10 years would indicate extraordinarily fast cooling of the NS that can be regulated by superfluidity of nucleons in the stellar core.

Author: Reux, C. et al.; Genre: Journal Article; Issued: 2015; Keywords: A corrigendum for this article has been published in 2015 Nucl. Fusion 55 129501; Title: Runaway electron beam generation and mitigation during disruptions at JET-ILW

We report on the first experimental observation of topological edge states in zigzag chains of plasmonic nanodisks. We demonstrate that such edge states can be selectively excited with the linear polarization of the incident light, and visualize them directly by near-field scanning optical microscopy. Our work provides experimental verification of a novel paradigm for manipulating light at the nanoscale in topologically nontrivial structures.

Maunder Minimum forms an archetype for the Grand minima, and detailed knowledge of its temporal development has important consequences for the solar dynamo theory dealing with long-term solar activity evolution. Here we reconsider the current paradigm of the Grand minimum general scenario by using newly recovered sunspot observations by G. Marcgraf and revising some earlier uncertain data for the period 1636--1642, i.e., one solar cycle before the beginning of the Maunder Minimum. The new and revised data dramatically change the magnitude of the sunspot cycle just before the Maunder Minimum, from 60--70 down to about 20, implying a possibly gradual onset of the Minimum with reduced activity started two cycles before it. This revised scenario of the Maunder Minimum changes, through the paradigm for Grand solar/stellar activity minima, the observational constraint on the solar/stellar dynamo theories focused on long-term studies and occurrence of Grand minima.

Abstract The purpose of the present review article is to give an outline of a quasiclassical approach to the description of transport in superconductors. The Boltzmann equation for normal excitation in a superconductor is formulated and its various properties are discussed and a full set of equations to describe condensate dynamics in the presence of external fields is given. Applications of this approach are demonstrated with a number of examples.